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Article
Thermal Characteristics of a Beaver Dam Analogues Equipped
Spring-Fed Creek in the Canadian Rockies
Tariq M. Munir * and Cherie J. Westbrook
Citation: Munir, T.M.; Westbrook,
C.J. Thermal Characteristics of a
Beaver Dam Analogues Equipped
Spring-Fed Creek in the Canadian
Rockies. Water 2021,13, 990. https://
doi.org/10.3390/w13070990
Academic Editor: David Dunkerley
Received: 24 February 2021
Accepted: 1 April 2021
Published: 3 April 2021
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
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iations.
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Department of Geography and Planning, Centre for Hydrology, University of Saskatchewan,
Saskatoon, SK S7N 5C8, Canada; cherie.westbrook@usask.ca
*Correspondence: tariq.munir@usask.ca; Tel.: +1-4039715639
Abstract:
Beaver dam analogues (BDAs) are becoming an increasingly popular stream restoration
technique. One ecological function BDAs might help restore is suitable habitat conditions for fish in
streams where loss of beaver dams and channel incision has led to their decline. A critical physical
characteristic for fish is stream temperature. We examined the thermal regime of a spring-fed Cana-
dian Rocky Mountain stream in relation to different numbers of BDAs installed in series over three
study periods (April–October; 2017–2019). While all BDA configurations significantly influenced
stream and pond temperatures, single- and double-configuration BDAs incrementally increased
stream temperatures. Single and double configuration BDAs warmed the downstream waters of
mean maxima of 9.9, 9.3
◦
C by respective mean maxima of 0.9 and 1.0
◦
C. Higher pond and stream
temperatures occurred when ponding and discharge decreased, and vice versa. In 2019, variation in
stream temperature below double-configuration BDAs was lower than the single-configuration BDA.
The triple-configuration BDA, in contrast, cooled the stream, although the mean maximum stream
temperature was the highest below these structures. Ponding upstream of BDAs increased discharge
and resulted in cooling of the stream. Rainfall events sharply and transiently reduced stream temper-
atures, leading to a three-way interaction between BDA configuration, rainfall and stream discharge
as factors co-influencing the stream temperature regime. Our results have implications for optimal
growth of regionally important and threatened bull and cutthroat trout fish species.
Keywords: stream temperature; stream restoration; BDA; ecohydrology; cutthroat trout; bull trout
1. Introduction
Beavers (Caster canadensis and C. fiber) are ubiquitously considered as aquatic ecosys-
tem engineers in recognition of the ecosystem functions provided by their dams [
1
–
4
].
Changes in the streamflow regime can lead to channel aggradation [
5
,
6
]. In streams from
which beavers have been lost via removal or relocation, channels incise and riparian ar-
eas ecologically degrade [
7
,
8
]. When streams have degraded to the point that they are
inhospitable for beavers, beaver dam analogues (BDAs) are used as a low-cost, low-tech
restoration solutions [
9
–
12
]. BDAs can be installed in a variety of configurations, ranging
from individual structures to multiple structures in sequence [
13
,
14
], the goal of which is
ensuring some BDAs persist following larger flow events [4].
One critical restoration priority for degraded streams is the moderation of high water
temperatures [
12
]. Temperature is a key environmental variable regulating phenology,
metabolism, and acclimation of aquatic species [
15
–
17
] including cold-water fish [
18
].
Streams that are degraded have higher temperatures [
19
,
20
] that may severely limit the
life processes of cold-water fish or result in mortality due to the high cost of metabolic
maintenance [
21
]. In the Canadian Rocky Mountains, westslope cutthroat trout (On-
corhynchus clarki lewisi) and bull trout (Salvelinus confluentus) are recognized as threatened
species [
22
,
23
]. The thermal tolerance range of both fish species is 8 to 19
◦
C, with sustained
temperatures >19.6 ◦C identified as lethal [18,24].
Water 2021,13, 990. https://doi.org/10.3390/w13070990 https://www.mdpi.com/journal/water
Water 2021,13, 990 2 of 14
BDAs, similar to beaver dams, pool stream water and enhance groundwater-surface
water interactions [
25
]. These ecohydrological changes can impact the overall stream
temperature regime. The literature describing how beaver dams and BDAs influence the
thermal regime of streams is sparse and inconsistent. Some studies conclude that beaver
dams increase overall downstream temperature [
18
,
26
], with increases ranging from as
little as 0.4
◦
C to 3.6
◦
C [
27
–
29
] to as much as 7.0
◦
C [
30
]. Other studies come to mixed
conclusions on whether dams warm or cool streams, citing dam height as an important
distinguishing factor. Fuller and Peckarsky [
31
], for example, reported that downstream
warming occurred below low dams and under low stream velocity compared to cool-
ing that occurred below high-headed dams and under higher stream velocity conditions.
Other studies have reported cooling downstream beaver dam complexes [
28
]. A study at
Bridge Creek, Oregon for example, reported that BDAs buffered summer stream temper-
ature extremes and created temperature refugia important for salmonoids [
20
]. Further,
Lautz et al. [
32
] argued that ponding by BDAs may increase downstream surface area
and subsequently temperature; however, surface water-groundwater exchanges around
BDA and associated increased vegetation shading may lead to lower and less variable
stream temperatures.
What the research on BDAs indicates is that a deeper understanding of how they
influence various hydrologically and ecologically important processes is needed, including
the thermal regime of streams. Studying the process responses of BDAs in different climates
and hydrogeomorphic settings and comparing results will aid in developing guidance for
practitioners on how to best use this stream restoration tool. Thus, the goal of our study
was to evaluate the effects of different BDA configurations on the stream temperature
regime. We hypothesized that the stream would be warmed by the use of BDAs, and
that the warming effect would be magnified by installing a greater number of BDAs in
sequence. Study results will be useful for those in management who may be considering
the installation of BDAs, especially on streams that provide habitat to temperature-sensitive
fish species.
2. Materials and Methods
2.1. Study Area
The study was conducted in Ann and Sandy Cross Conservation Area (ASCCA),
a 19.4 km
2
nature preserve of the rolling foothills of the Canadian Rocky Mountains in
western Alberta. There are several perennial springs on ASCCA which drain eastward
on Pine Creek to Fish Creek, which is a tributary of the Bow River. Dominant hydro-
geology of the area is comprised of Paskapoo formation, which is an extensive fluvial
sandstone and mudstone complex in the Western Canadian sedimentary basin and re-
ported to support more groundwater wells than any other aquifer system in the Canadian
Prairies [
33
]. The overstory comprises trembling aspen (Populus tremuloides), balsam poplar
(Populus balsamifera), blue spruce (Picea pungens), white spruce (Picea glauca), flowering al-
mond (Prunus triloba), lodgepole pine (Pinus contorta), mugo pine (Pinus mugo), paper birch
(Betula papynifera), Siberian crabapple (Malus baccata) and water birch (Betula occidentalis).
The understory comprises prickly rose (Rosa acicularis) and snowberry (Symphoricarpos
albus) shrubs mixed with bluejoint (Calamagrostis canadensis), smooth brome (Bromus inermis
ssp. Inermis), small bottle sedge (Carexutriculata) and northern reed (Calamagrostis stricata
spp. Inexpansa) [
25
]. Thirty-year (1981–2010) mean seasonal (May–October) air temperature
(T_air) and precipitation normals in the region are 12.2 ◦C and 63.5 mm, respectively.
Historically, Pine Creek, the upstream reach of Fish Creek, has been a beaver habi-
tat [
34
]; remnant beaver dams along Pine Creek are still visible. Southern arm of the Pine
Creek once had a trout farm. An electrofishing survey [
35
] found that the two most abun-
dant native trout species in the Fish Creek were westslope cutthroat trout (Oncorhynchus
clarkii lewisi) and bull trout (Salvelinus confluentus). Beavers were lost from the area by the
early 1990s because of illegal trapping or relocation (G. Shyba, pers. comm.). In the absence
of beaver, Pine Creek has degraded—the stream is incised, and Salix spp. shrubs are either
Water 2021,13, 990 3 of 14
dead or severely degraded. The fish population in the lower Bow River fell by an average of
46.5% during 2003–2013 in response to the potential stressors of whirling disease, flooding,
and release mortality [
36
]. The Alberta Institute for Wildlife Conservation in collaboration
with site management attempted to rewild ASCCA with the native beaver species; a pair
of beavers was introduced on 18 May 2016 [37] but not to Pine Creek.
2.2. Methods
We studied a 1075-m long reach of the north arm of Pine Creek in the ice-free period
of May-October in 2017, 2018 and 2019. The reach has an average stream width of 0.63 m,
an approximate elevation of 1150 m (asl) and N–W and W–E slopes of 0.21% and 1.22%,
respectively. A total of six BDA structures were installed in the study reach 3–9 August in
2018. The BDAs were in single (BDA6), double (BDA2, BDA1) and triple (BDA5, BDA4,
BDA3) configurations. Further details on BDA construction, materials and installation are
explained by Munir and Westbrook [25].
Stream temperature and stage were monitored at four locations in the study reach in
the thalweg, starting in May 2018. Four stream gauges (SG4–SG1; stage at each measured
with a levelogger junior 3001, Solinst, ON, Canada) were installed such that SG4 was
at the upstream of BDA6 and SG3–SG1 were installed downstream of each of the three
BDA configurations (Figure 1). Stage was converted to discharge using a rating curve.
Streamflow data were also measured in 2017 before the BDAs were installed, but only at
SG1. The stream stage and temperature at each SG were measured at 15-min intervals,
corrected for barometric pressure, and averaged by the three BDA configurations.
Water 2021, 13, x FOR PEER REVIEW 3 of 15
Creek once had a trout farm. An electrofishing survey [35] found that the two most abun-
dant native trout species in the Fish Creek were westslope cutthroat trout (Oncorhynchus
clarkii lewisi) and bull trout (Salvelinus confluentus). Beavers were lost from the area by
the early 1990s because of illegal trapping or relocation (G. Shyba, pers. comm.). In the
absence of beaver, Pine Creek has degraded—the stream is incised, and Salix spp. shrubs
are either dead or severely degraded. The fish population in the lower Bow River fell by
an average of 46.5% during 2003–2013 in response to the potential stressors of whirling
disease, flooding, and release mortality [36]. The Alberta Institute for Wildlife Conser-
vation in collaboration with site management attempted to rewild ASCCA with the na-
tive beaver species; a pair of beavers was introduced on 18 May 2016 [37] but not to Pine
Creek.
2.2. Methods
We studied a 1075-m long reach of the north arm of Pine Creek in the ice-free period
of May-October in 2017, 2018 and 2019. The reach has an average stream width of 0.63
m, an approximate elevation of 1150 m (asl) and N–W and W–E slopes of 0.21% and
1.22%, respectively. A total of six BDA structures were installed in the study reach 3–9
August in 2018. The BDAs were in single (BDA6), double (BDA2, BDA1) and triple
(BDA5, BDA4, BDA3) configurations. Further details on BDA construction, materials
and installation are explained by Munir and Westbrook [25].
Stream temperature and stage were monitored at four locations in the study reach
in the thalweg, starting in May 2018. Four stream gauges (SG4–SG1; stage at each meas-
ured with a levelogger junior 3001, Solinst, ON, Canada) were installed such that SG4
was at the upstream of BDA6 and SG3–SG1 were installed downstream of each of the
three BDA configurations (Figure 1). Stage was converted to discharge using a rating
curve. Streamflow data were also measured in 2017 before the BDAs were installed, but
only at SG1. The stream stage and temperature at each SG were measured at 15-min
intervals, corrected for barometric pressure, and averaged by the three BDA configura-
tions.
Figure 1. Study stream fitted with beaver dam analogue (BDA) configurations, pond gauges (PG) and stream gauges
(SG) at Ann and Sandy Cross Conservation Area, 30 km SW of Calgary in Alberta, Canada (50°51′ N, 114°13′ W). Six
BDAs (BDA6–BDA1) from upstream to downstream are represented by beige bars along ~1070 m long reach. 1–3 beige
bars show single-, double-, and triple-configurations, respectively. Each BDA is instrumented with an upstream PG
Figure 1.
Study stream fitted with beaver dam analogue (BDA) configurations, pond gauges (PG) and stream gauges (SG)
at Ann and Sandy Cross Conservation Area, 30 km SW of Calgary in Alberta, Canada (50
◦
51
0
N, 114
◦
13
0
W). Six BDAs
(BDA6–BDA1) from upstream to downstream are represented by beige bars along ~1070 m long reach. 1–3 beige bars
show single-, double-, and triple-configurations, respectively. Each BDA is instrumented with an upstream PG (PG6–PG1).
Four SGs (SG4–SG1, represented by red arrows) before or after each of the three configuration series monitored stream
stage/discharge. One surface spring fed the creek (tele-blue line). Reach and the Instrumentations are not up to the scale.
Temperature and level in the deepest part of the ponds formed by each of the six BDAs
(PG6–PG1) were measured during April–August 2019 with automatic loggers (levelogger
junior 3001, Solinst, ON, Canada) housed in perforated PVC pipes (length = 1.0 m; diame-
ter = 0.035 m) inserted into the stream bed [
18
,
26
]. Observations were collected at 15-min
intervals, levels were corrected for barometric pressure, and levels and temperature were
Water 2021,13, 990 4 of 14
averaged by the three BDA configurations. Rainfall observations were obtained from the
nearest Alberta Environment and Parks rain gauge at Priddis (Alberta station ID 3033505),
located 7.5 km west of the study reach at 1371 m elevation.
2.3. Data Analysis
SPSS 26.0 package (SPSS, Chicago, IL, USA) was used for statistical analyses Landau
and Everitt [
38
]. Two separate linear mixed-effects models (LMEM) were performed to
predict the fluctuations in stream and pond temperatures in response to the fixed effects of
BDA-configuration (single, double, triple), stream discharge, rainfall and BDA pond level.
A random effect of BDA configuration was used to test the effects of upstream/downstream
configurations on the predictor and outcome variables. It was assured that any significant
interactions between rainfall and other predictors (stream discharge, BDA pond level) were
not only the result of collinearity. A compound symmetry covariance structure was used
in all LMEM applications. Daily mean changes in stream temperature values (
∆
T) were
obtained by subtracting daily downstream values from corresponding upstream values;
these data were used in the model. Before analyses, all data were tested for normality
and homogeneity of variance using the Kolmogorov–Smirnov test and Levene’s test,
respectively. Regressions and 1:1 fit (s) were performed to validate the models developed.
A significance level of 95% (p< 0.05) and/or LogWorth (-log10(p); p< 0.01) was used. The
goodness of fit was reported as R
2
value. Temporally paired t-tests were used to compare
stream temperatures before and after BDA installations. One-way analysis of variance
(ANOVA) and/or Tukey’s Post hoc test were used, when needed, to explain differences
in stream or pond maximum temperatures (T
max
) for different BDA configurations. The
Holm–Sidak method was used to test the differences in means when the data used was
not normally distributed. The downstream—upstream difference in temperature (∆T) for
the three BDA configurations were obtained by using the raw temperatures logged at
15-minute intervals across the study reach/years; these data were used for drawing density
curves for ∆T.
3. Results
Mean seasonal (May–October) air temperature for the 2017-18-19 study years fell lin-
early from 12.3 to 11.7 to 11.5
◦
C, respectively, coincident with decreases in maximum air
temperatures from 20.9 to 17.8 to 17.2
◦
C. However, seasonal minimum temperature in-
creased in the study years from 3.7 to 5.6 to 5.8
◦
C. Seasonal rainfall was lowest (160 mm) in
2017, higher in 2018 (277 mm) and highest in 2019 (317 mm). Rainfall influenced T_air during
storm events (Figure 2; ANOVA: F
1,169
= 5.73, p= 0.018, R
2
= 0.03). T_air had a significant
influence on the overall stream temperature both pre- (ANOVA: F
1,70
= 159.44, p< 0.001,
R2= 0.80) and post-BDA (ANOVA: F1,169 = 350.40, p< 0.001, R2= 0.68) installations.
Water 2021, 13, x FOR PEER REVIEW 5 of 15
ation of 9.2–14.9 °C for the same period, before BDA installation. No difference in ther-
mal variation between the two years was found (ANOVA: F1,102 = 0.45, p = 0.499). Rainfall
had only a weak effect on stream temperature (ANOVA: F1,302 = 686.37, p < 0.001, R2 =
0.02).
Figure 2. Daily stream thermograph at SG1 (black line is mean, grey area is range) and hyetograph for pre-BDA instal-
lation period (2017–2018).
After the BDAs were installed in August 2018, mean daily stream temperature in-
creased longitudinally downstream, from 7.5 °C at SG4 to 8.4 °C at SG1 (Figure 3).
Higher daily thermal variation was found below singularly configured BDA than down-
stream of the double and triple configuration BDAs. Single and double configurations
contributed to warming downstream by 0.38 and 0.76 °C , respectively, converse to the
triple configuration which aided in cooling the downstream by 0.24 °C . Increases in
stream velocity also cooled the downstream of any configuration.
Single and double configuration BDAs showed overall positive ΔT through 2018–
2019, indicating net warming of stream water as it passed through the BDA. In contrast,
the triple configuration BDAs largely had negative ΔT, indicating net cooling of water
as it passed through the BDA sequence, especially in 2019 (Figure 4). The disparities in
ΔT distribution densities for the three BDA configurations across the two BDA years are
illustrated in Figure 5. Triple configuration BDAs showed the most variation in ΔT fol-
lowed by the double and single configurations in that order. Also, the triple and double
configurations had bimodal distributions, with the different peaks corresponding to the
overall warmer 2018 and cooler 2019.
Maximum temperatures (Tmax) of stream water below BDA configurations were
compared by applying one-way ANOVA; Tmax below the triple configuration was signif-
icantly higher than below the double and single configurations, which had similar Tmax
(Table 1). Temporal, paired t-test comparisons (pre- vs. post-BDA installation) were per-
formed to determine if the various BDA configurations influenced downstream temper-
ature differently. In comparing the same day’s stream temperature data logged at SG4–
SG1 across the pre- and post-BDA installation years, we found that downstream tem-
peratures were significantly reduced after BDA installation (Table 1); Post-installation
reductions below single, double, and triple BDAs were 1.5, 3.8 and 1.6 °C, respectively.
Stream temperatures below the BDAs were mostly in the safe range (<10–12 °C ) for
westslope cutthroat and bull trout species, although triple configuration offered transi-
ently largest range of temperatures with warmer conditions over an extended period
across the two years (Table 2). No lethal temperature (≥19.6 °C ) occurred below any con-
figuration at any time.
Stream temp. (°C)
5
10
15
20
Rainfall (bars; mm)
0
10
20
30
40
SG1
14
Jun 14
Jul 13
Aug 13
May 13
Jun 13
Jul
2017 2018
5
Aug
Figure 2.
Daily stream thermograph at SG1 (black line is mean, grey area is range) and hyetograph for pre-BDA installation
period (2017–2018).
Water 2021,13, 990 5 of 14
3.1. Stream Temperature
Before BDAs installation (2017), mean daily stream temperature at SG1 was 12.0
◦
C
with a daily average range of 9.2–15.8
◦
C during June 4-August 4 (Figure 2). In 2018, mean
daily temperature was cooler by 0.2 (11.8
◦
C) with an average daily thermal variation of
9.2–14.9
◦
C for the same period, before BDA installation. No difference in thermal variation
between the two years was found (ANOVA: F
1,102
= 0.45, p= 0.499). Rainfall had only a
weak effect on stream temperature (ANOVA: F1,302 = 686.37, p< 0.001, R2= 0.02).
After the BDAs were installed in August 2018, mean daily stream temperature in-
creased longitudinally downstream, from 7.5
◦
C at SG4 to 8.4
◦
C at SG1 (Figure 3). Higher
daily thermal variation was found below singularly configured BDA than downstream of
the double and triple configuration BDAs. Single and double configurations contributed to
warming downstream by 0.38 and 0.76
◦
C, respectively, converse to the triple configuration
which aided in cooling the downstream by 0.24
◦
C. Increases in stream velocity also cooled
the downstream of any configuration.
Water 2021, 13, x FOR PEER REVIEW 6 of 15
Figure 3. Daily ambient air temperature range (black line is mean, grey area is range) and hyetograph (top panel), and
daily stream thermographs at SG4-SG1 (bottom four panels) across the pine creek study reach for the post-BDA instal-
lation period (2018–2019).
0
5
10
15
0
5
10
15
0
5
10
15
Streamflow
---------Stream temperature (°C)---------
0
5
10
15
Air temperature (°C)
-10
0
10
20
30
40
Rainfall (bars; mm)
0
20
40
60
SG4
SG3
SG2
SG1
5
Aug 3
Sep 3
Oct 13
May 13
Jun 13
Jul
2018 2019
20
Apr 5
Aug
Figure 3.
Daily ambient air temperature range (black line is mean, grey area is range) and hyetograph
(top panel), and daily stream thermographs at SG4-SG1 (bottom four panels) across the pine creek
study reach for the post-BDA installation period (2018–2019).
Water 2021,13, 990 6 of 14
Single and double configuration BDAs showed overall positive
∆
T through 2018–2019,
indicating net warming of stream water as it passed through the BDA. In contrast, the triple
configuration BDAs largely had negative
∆
T, indicating net cooling of water as it passed
through the BDA sequence, especially in 2019 (Figure 4). The disparities in
∆
T distribution
densities for the three BDA configurations across the two BDA years are illustrated in
Figure 5. Triple configuration BDAs showed the most variation in
∆
T followed by the
double and single configurations in that order. Also, the triple and double configurations
had bimodal distributions, with the different peaks corresponding to the overall warmer
2018 and cooler 2019.
Water 2021, 13, x FOR PEER REVIEW 7 of 15
Figure 4. Difference in temperature (ΔT; downstream—upstream) for different BDA configurations used over the 2018–
2019 post-BDA installation period (2018–2019).
BDA configuration, stream discharge and pond level were significant predictors
responsible for explaining variations in downstream temperatures (Table 1). Rainfall
events sharply and transiently reduced stream temperatures, leading to a three-way in-
teraction between BDA-configuration, rainfall and stream discharge influencing the
stream temperature regime. Stream discharge was the strongest control over variations
in downstream temperatures followed by BDA configuration and pond depth in that
order.
Figure 4.
Difference in temperature (
∆
T; downstream—upstream) for different BDA configurations
used over the 2018–2019 post-BDA installation period (2018–2019).
Water 2021,13, 990 7 of 14
Water 2021, 13, x FOR PEER REVIEW 8 of 15
Figure 5. Differential stream temperature (downstream–upstream) densities for the BDA configurations over the post-
BDA installation period (2018–2019).
3.2. Pond Temperature
Overall, mean daily pond temperature was higher with more BDAs in sequence
(single = 7.7 °C ; triple = 8.0 °C ; p < 0.001). Thermal variation in the pond formed by the
single configuration BDA (6.2–9.3 °C) was higher than in the ponds formed by the dou-
ble (6.9–9.4 °C ) and triple (6.7–9.7 °C) configuration BDAs (Figure 6). A one-way
ANOVA compared pond Tmax values from three BDA configurations. Tmax in ponds
formed by the BDAs in the triple configuration was significantly higher than in the
ponds formed by the double and single configuration BDAs, which were similar (Table
1). BDA configuration, stream discharge, BDA pond depth and rainfall were significant
predictors responsible for variation in BDA pond temperature between 6.2–9.7 °C (Table
1). While installing multiple BDAs in sequence magnified the increase in upstream pond
temperature; these increases were moderated by increases in stream velocity and pond
level or by rainfall events.
Results of a LMEM for stream temperature were also validated by a linear regres-
sion model for demonstrating how BDA configuration, stream discharge, rainfall and
pond depth had controls on stream temperature (Figure 7A). The separate linear regres-
sion model demonstrated strong interrelationships among BDA configuration, stream
discharge, rainfall, pond depth and pond temperature (Figure 7B).
Figure 5.
Differential stream temperature (downstream–upstream) densities for the BDA configura-
tions over the post-BDA installation period (2018–2019).
Maximum temperatures (T
max
) of stream water below BDA configurations were com-
pared by applying one-way ANOVA; T
max
below the triple configuration was significantly
higher than below the double and single configurations, which had similar T
max
(Table 1).
Temporal, paired t-test comparisons (pre- vs. post-BDA installation) were performed to de-
termine if the various BDA configurations influenced downstream temperature differently.
In comparing the same day’s stream temperature data logged at SG4–SG1 across the pre-
and post-BDA installation years, we found that downstream temperatures were significantly
reduced after BDA installation (Table 1); Post-installation reductions below single, double, and
triple BDAs were 1.5, 3.8 and 1.6 ◦C, respectively.
Stream temperatures below the BDAs were mostly in the safe range (<10–12
◦
C) for
westslope cutthroat and bull trout species, although triple configuration offered transiently
largest range of temperatures with warmer conditions over an extended period across the
two years (Table 2). No lethal temperature (
≥
19.6
◦
C) occurred below any configuration at
any time.
BDA configuration, stream discharge and pond level were significant predictors re-
sponsible for explaining variations in downstream temperatures (Table 1). Rainfall events
sharply and transiently reduced stream temperatures, leading to a three-way interaction
between BDA-configuration, rainfall and stream discharge influencing the stream tempera-
ture regime. Stream discharge was the strongest control over variations in downstream
temperatures followed by BDA configuration and pond depth in that order.
Water 2021,13, 990 8 of 14
Table 1.
Statistical analyses results of (1) paired t-comparisons between pre- and post-BDA treatment stream temperatures,
(2) One-way analyses of variance (ANOVAs) for daily pond mean maximum temperatures (Tmax), and (3) two mixed-effects
models with fixed effects of BDA configuration (single, double, triple), stream discharge, rainfall and BDA pond level, a
random effect of BDA configuration, and an outcome variable of stream or pond temperature, over the 2017–2019 study
periods †.
Effect/Term Stream Temp. (◦C) BDA Pondwater Temp. (◦C)
df F or t-Ratio
p/
LogWorth
(-log10(p))
df F or t-Ratio
p/
LogWorth
(-log10(p))
PAIRED t-TESTS (Pre- vs. post-BDA installation)
T_1-config. (2018–2019; R2= 0.57) 107 5.36 <0.001
n/a
T_2-config. (2018–2019; R2= 0.15) 107 11.41 <0.001
T_2-config. (2017–2019; R2= 0.11) 107 12.31 <0.001
T_3-config. (2018–2019; R2= 0.84) 107 7.92 <0.001
Tmax one-way ANOVA (Holm–Sidak method)
(1-config. = 8.3 ◦C) vs. (2-config. = 9.0 ◦C) 175 −1.81 0.070 96 0.23 0.822
(1-config. = 8.3 ◦C) vs. (3-config. = 9.9 ◦C) 169 −4.12 <0.001 98 −2.36 0.038
(2-config. = 9.0 ◦C) vs. (3-config. = 9.9 ◦C) 169 −2.30 <0.042 96 −2.59 0.030
MIXED-EFFECTS MODELS (Stepwise Regressions)
BDA configuration 2,2 13.99 <0.001/
8.17 2,2 21.36 <0.001/
8.65
(T_1-config.)-(T_2-config.) - −2.43 0.071 - −1.14 0.601
(T_1-config.)-(T_3-config.) - −6.07 <0.001 -−5.63 <0.001
(T_2-config.)-(T_3-config.) - −2.71 0.034 -−4.12 <0.001
Stream discharge 1,1 −10.51 <0.001/
23.56 1,1 −6.13 <0.001/
8.53
Rainfall 1,1 −0.58 0.565 1,1 −2.06 0.041
BDA pondwater level 1,1 −3.69 <0.001/
3.57 1,1 −3.46 <0.001/
3.20
Stream discharge ×Rainfall 1,1 4.43 <0.001 1,1 3.79 <0.001
BDA-config. ×Stream discharge ×Rainfall 2,2 4.80 0.003 2,2 2.25 0.025
†
1-config., 2-config., 3-config. represent single- double and triple configurations, respectively. Pre- and post-treatment periods are between
20 April and 5 August/2017, 2018, 2019. T
max
period is between 5 August 2018 and 5 August 2019 for stream temperature and 29 April and
5 August 2019 for pond temperatures. A LogWorth value of >2.0 signifies 0.01 level ((-log10(0.01) = 2) and provides strength of significance
with greater the value more the strength. pvalues are significant at <0.05. The maximum of three-way interaction when significant is
retained in the stepwise regression method to keep the brevity of model results.
Table 2.
Percent of hours summer stream temperatures fell into one of the five temperature ranges
downstream of three BDA configuration series. Maximum growth temperature for bull trout is
13.2
◦
C with an acclimation temperature range of 8–19.6
◦
C. The optima zone for westslope cutthroat
trout is 13–15
◦
C while consistent temperatures above 19.6
◦
C are lethal. Site locations are shown in
Figure 1†.
Year BDA
Configuration
Total Hours
Sampled
Percent of Total Hours in Temperature Range (◦C)
<10 10–12 13–15 16–19.5 ≥19.6
2018 Single 2776 62 34 4 0 0
Double 3258 45 29 20 6 0
Triple 2775 48 37 4 11 0
2019 Single 2570 69 20 10 1 0
Double 2572 64 36 0 0 0
Triple 2571 72 23 3 2 0
†
summer stream temperature dates ranged between 5 August 2018, and 5 August 2019 (post-BDA installation pe-
riod).
3.2. Pond Temperature
Overall, mean daily pond temperature was higher with more BDAs in sequence
(single = 7.7
◦
C; triple = 8.0
◦
C; p< 0.001). Thermal variation in the pond formed by the
Water 2021,13, 990 9 of 14
single configuration BDA (6.2–9.3
◦
C) was higher than in the ponds formed by the double
(6.9–9.4
◦
C) and triple (6.7–9.7
◦
C) configuration BDAs (Figure 6). A one-way ANOVA
compared pond T
max
values from three BDA configurations. T
max
in ponds formed by the
BDAs in the triple configuration was significantly higher than in the ponds formed by the
double and single configuration BDAs, which were similar (Table 1). BDA configuration,
stream discharge, BDA pond depth and rainfall were significant predictors responsible for
variation in BDA pond temperature between 6.2–9.7
◦
C (Table 1). While installing multiple
BDAs in sequence magnified the increase in upstream pond temperature; these increases
were moderated by increases in stream velocity and pond level or by rainfall events.
Water 2021, 13, x FOR PEER REVIEW 10 of 15
Figure 6. Daily pond temperatures for the three different BDA configurations over the 2019 post-BDA installation pe-
riod.
Figure 7. Impacts of BDA configuration, stream discharge, BDA pond level and rainfall on stream temperature (A) and
BDA pond temperature (B) using a linear mixed model and compared to a 1:1 line. Goodness of model fit (R2) between
modelled and observed values are shown in each case.
Overall, the changes in downstream temperature in response to upstream pond
level were complex. For example, increases in pond level led to decreases in stream tem-
perature. The relationship between pond depth-stream temperature was further inves-
tigated using quadratic curves (Figure 8). Temperatures downstream of the BDA struc-
tures showed a complex relationship with BDA pond depths: stream temperature in-
creased non-linearly with increasing pond depths up to 0.27 m for single, and 0.37 m for
double and triple configurations, and then decreased non-linearly for further pond in-
creases (Figure 8A). Cooling of pond was concurrent to rising of the level that was di-
rectly related to rainfall (p < 0.001). Pond temperature also had a threshold response to
Observed
0 2 4 6 8 10 12 14
Modelled
0
2
4
6
8
10
12
14
Observed
0 2 4 6 8 10 12 14
Modelled
0
2
4
6
8
10
12
14
AB
Y = 2.688-10X; RMSE = 0.203
Adj. R2 = 0.99; p<0.001 Y = 1.190-10X; RMSE = 0.207
Adj. R2 = 0.99; p<0.001
Figure 6.
Daily pond temperatures for the three different BDA configurations over the 2019 post-BDA
installation period.
Results of a LMEM for stream temperature were also validated by a linear regression
model for demonstrating how BDA configuration, stream discharge, rainfall and pond
depth had controls on stream temperature (Figure 7A). The separate linear regression
model demonstrated strong interrelationships among BDA configuration, stream discharge,
rainfall, pond depth and pond temperature (Figure 7B).
Overall, the changes in downstream temperature in response to upstream pond level
were complex. For example, increases in pond level led to decreases in stream temperature.
The relationship between pond depth-stream temperature was further investigated using
quadratic curves (Figure 8). Temperatures downstream of the BDA structures showed a
complex relationship with BDA pond depths: stream temperature increased non-linearly
with increasing pond depths up to 0.27 m for single, and 0.37 m for double and triple
configurations, and then decreased non-linearly for further pond increases (Figure 8A).
Cooling of pond was concurrent to rising of the level that was directly related to rainfall
(p< 0.001). Pond temperature also had a threshold response to upstream pond depth
wherein pond temperature non-linearly increased with increasing pond depth up to the
thresholds of 0.28 m for single, and 0.38 m for double and triple configurations, and then
fell steeply at a rate identical to the cooling rate of downstream waters (Figure 8B).
Water 2021,13, 990 10 of 14
Water 2021, 13, x FOR PEER REVIEW 10 of 15
Figure 6. Daily pond temperatures for the three different BDA configurations over the 2019 post-BDA installation pe-
riod.
Figure 7. Impacts of BDA configuration, stream discharge, BDA pond level and rainfall on stream temperature (A) and
BDA pond temperature (B) using a linear mixed model and compared to a 1:1 line. Goodness of model fit (R2) between
modelled and observed values are shown in each case.
Overall, the changes in downstream temperature in response to upstream pond
level were complex. For example, increases in pond level led to decreases in stream tem-
perature. The relationship between pond depth-stream temperature was further inves-
tigated using quadratic curves (Figure 8). Temperatures downstream of the BDA struc-
tures showed a complex relationship with BDA pond depths: stream temperature in-
creased non-linearly with increasing pond depths up to 0.27 m for single, and 0.37 m for
double and triple configurations, and then decreased non-linearly for further pond in-
creases (Figure 8A). Cooling of pond was concurrent to rising of the level that was di-
rectly related to rainfall (p < 0.001). Pond temperature also had a threshold response to
Observed
0 2 4 6 8 10 12 14
Modelled
0
2
4
6
8
10
12
14
Observed
0 2 4 6 8 10 12 14
Modelled
0
2
4
6
8
10
12
14
AB
Y = 2.688-10X; RMSE = 0.203
Adj. R2 = 0.99; p<0.001 Y = 1.190-10X; RMSE = 0.207
Adj. R2 = 0.99; p<0.001
Figure 7.
Impacts of BDA configuration, stream discharge, BDA pond level and rainfall on stream
temperature (
A
) and BDA pond temperature (
B
) using a linear mixed model and compared to a 1:1
line. Goodness of model fit (R2) between modelled and observed values are shown in each case.
Water 2021, 13, x FOR PEER REVIEW 11 of 15
upstream pond depth wherein pond temperature non-linearly increased with increasing
pond depth up to the thresholds of 0.28 m for single, and 0.38 m for double and triple
configurations, and then fell steeply at a rate identical to the cooling rate of downstream
waters (Figure 8B).
Figure 8. Relationships of daily BDA Pond depth with respective stream (A) and pond (B) temperatures to show the role
of ponding on the respective temperature regimes above or below different BDA configurations.
4. Discussion
The BDAs modified stream and pond temperatures along the studied reach of Pine
Creek in ways consistent with how beaver dams are known to modify stream tempera-
tures. Having more BDAs installed in a sequence generally enhanced warming of stream
and pond temperatures. However, we also noted that diffuse spring inputs to the stream
at the location of the triple-configuration BDA counteracted the warming influence of it.
Our findings have important implications for those in aquatic ecosystem management
who may be considering the installation of BDAs for restoring downstream ecosystems
for cold water fish species.
4.1. Stream and Pond Temperatures
Stream temperature modification is one of the effects of natural beaver dams and
has been frequently reported; however, the literature describing how beaver dams in-
fluence the thermal regime is inconsistent, perhaps owing to study of different spatial
and/or temporal scales. The BDA configurations we used altered downstream tempera-
ture regime compared to no changes in stream temperature for pre-installation years.
Overall, mean temperature and Tmax increased and the thermal variation (Trange) de-
creased from upstream to downstream post-installation of BDAs or during 2018–2019.
Our results are consistent with some studies of beaver dam and BDA impacts on stream
temperature but contrary to the findings of other studies. As at Pine Creek, beaver dams
studied by Andersen, Shafroth, Pritekel and O’Neill [26], Majerova, Neilson, Schmadel,
Wheaton and Snow [27], Fuller and Peckarsky [31], Shetter and Whalls [29], report
downstream warming of stream water. Other studies show only partially offsetting of
daytime thermal extremes [12,20] or cooling [28,31] downstream of beaver dams. BDAs
are intended to mimic similar functions of natural beaver dams [20]. However, few data
on BDA-induced stream temperature alteration are available to compare our findings
[12,20].
Figure 8.
Relationships of daily BDA Pond depth with respective stream (
A
) and pond (
B
) tempera-
tures to show the role of ponding on the respective temperature regimes above or below different
BDA configurations.
4. Discussion
The BDAs modified stream and pond temperatures along the studied reach of Pine
Creek in ways consistent with how beaver dams are known to modify stream temperatures.
Having more BDAs installed in a sequence generally enhanced warming of stream and
pond temperatures. However, we also noted that diffuse spring inputs to the stream at the
location of the triple-configuration BDA counteracted the warming influence of it. Our
findings have important implications for those in aquatic ecosystem management who
may be considering the installation of BDAs for restoring downstream ecosystems for cold
water fish species.
4.1. Stream and Pond Temperatures
Stream temperature modification is one of the effects of natural beaver dams and has
been frequently reported; however, the literature describing how beaver dams influence
the thermal regime is inconsistent, perhaps owing to study of different spatial and/or
temporal scales. The BDA configurations we used altered downstream temperature regime
Water 2021,13, 990 11 of 14
compared to no changes in stream temperature for pre-installation years. Overall, mean
temperature and T
max
increased and the thermal variation (T
range
) decreased from upstream
to downstream post-installation of BDAs or during 2018–2019. Our results are consistent
with some studies of beaver dam and BDA impacts on stream temperature but contrary
to the findings of other studies. As at Pine Creek, beaver dams studied by Andersen,
Shafroth, Pritekel and O’Neill [
26
], Majerova, Neilson, Schmadel, Wheaton and Snow [
27
],
Fuller and Peckarsky [
31
], Shetter and Whalls [
29
], report downstream warming of stream
water. Other studies show only partially offsetting of daytime thermal extremes [
12
,
20
] or
cooling [
28
,
31
] downstream of beaver dams. BDAs are intended to mimic similar functions
of natural beaver dams [
20
]. However, few data on BDA-induced stream temperature
alteration are available to compare our findings [12,20].
Ponding of stream water is a well-known effect of beaver dams [
39
]. Pond depth
regulates the temperature/stratification of the pond e.g., [e.g., 28] and downstream thermal
regime e.g., [e.g., 27,29]. Changing a free-flowing stream reach to one with pools and
riffles by adding beaver dams affects the stream energy balance [
40
], and it is expected
that BDA ponds would similarly affect on the stream energy balance. Generally, though,
beaver ponds are known to be important places for heat storage [
27
] due to the lowering
of the surface albedo. The resulting enhancements to short wave radiation absorption
are equivalent to the southward shift of a site by 7
◦
latitude [
40
] with a 0.73
◦
C increase
in temperature and 4.04 decrease in precipitation per degree of latitude reported for
Northern extratropical hemisphere 30–80
◦
N [
41
]. In our study, changes in pond and
stream temperatures in response to pond level were complex but consistent. For example,
increases in pond height were reflected in decreases in pond and stream temperatures as
demonstrated by our mixed-effects model. An additional robust investigation into the
relationships was performed by using Gaussian curves; we found that ponds warmed
with deepening up to the thresholds of 0.28 m for single, and 0.38 m for double and triple
configurations, and then started cooling for further pond level increases. The downstream
temperature was correlated to pond temperature, and driven by the pond depth. Shallow
beaver ponds increase the stream surface to volume ratio more than deeper ponds with the
smaller surface to volume ratios [
19
,
42
,
43
], which exposes shallow ponds to more radiant
energy [
19
,
42
]. A threshold pond depth for heating, however, has not been previously
reported. It is unlikely that although that residence time, which Schmadel, et al. [
44
] report
as a main control over pond temperature, was the key factor regulating pond temperature
at our site in that case deeper ponds with longer residence times would experience greater
heating. Pond warming can be (transiently) reversed by the addition of cooler groundwater
or rainfall inputs [20].
Alteration in daily temperature increased longitudinally downstream, and overall,
more BDAs in sequence increasingly warmed stream water. While Munir and West-
brook [
25
] observed that pond depth (and potentially surface area) increased with more
BDAs in sequence at this site, we found that overall pond temperature followed the suite
from single to triple configuration, though diel thermal variation decreased in that order.
These findings support the notion that increasing the number of BDAs increasingly influ-
ences downstream temperatures [
12
,
20
] by enhancing thermal groundwater exchanges
and/or radiant heat fluxes [
19
,
20
] similar to the function of natural beaver dams. Our
triple-configuration BDA did not warm the stream water as expected and instead cooled it
by 0.24
◦
C. The cooling may be related to an influx of spring water rather than the BDA
sequence itself. Munir and Westbrook [
25
] showed diffuse spring water entered the stream
at the location of the triple configuration BDA. Lateral cold-water seeps can cool stream
water [
45
], and may thus have obscured the warming influence of this BDA sequence. Since
the cooling by triple configuration was consistently less in magnitude than the warmings
created by the single (0.38
◦
C) and double (0.76
◦
C) configuration BDAs, net warming
of this BDA equipped small reach may be expected when no diffuse springs are present.
Further, downstream T
max
was highest below triple configuration followed by double and
single configurations in that order. Greater cumulative positive
∆
T (warming) of stream
Water 2021,13, 990 12 of 14
water as it passed through the single and double configurations compared to the negative
∆
T (cooling) for water that passed through triple configuration also fits with our finding of
overall increasing warming longitudinally downwards. Bimodal temperature distributions
reflected the overall differences in air temperature across the study years: overall warmer
2018 and cooler 2019. We recommend future studies characterize groundwater inflows to
stream reaches where BDAs are installed.
4.2. Mechanisms of Thermal Variation
One of the key controls on stream temperature below natural beaver dams or BDAs
could be the local hydrogeomorphic setting and/or weather patterns [
19
,
44
]. For example,
faster water and uneven and coarser substratum below beaver dams increased spatially
variable hydraulics and the amount of fluvial habitat heterogeneity available to native
fish in a stream network [
46
]. Spatially variable hydraulics [
46
] and residence time [
44
]
determined the amount of surface heat fluxes or albedo [
40
] and, therefore, downstream
temperatures for fish habitat heterogeneity. Warming downstream of natural beaver dams
or BDAs is reported more frequently than buffering or cooling. Since surface heat flux
influences pond and stream temperatures, downstream warming (to optimal tempera-
ture) below BDAs could be favourable to cold-water or stenothermal species in a cool
climate [
43
] compared to downstream warming (to lethal temperatures) in moderate or
warm climates [
18
]. McRae and Edwards [
18
] reported that streams containing beaver
ponds in Wisconsin, USA, averaged 7.6
◦
C warmer than streams without ponds—most
of the beaver streams exceeded thermal optima of 13–15
◦
C or fell into lethal range for
westslope cutthroat and bull trout. BDAs installed in Bridge-Creek, Oregon, USA, are
also reported to buffer daily thermal extremes or warm daily thermal minima during
summer [
20
]. However, these studies were carried out in a semi-arid region (46
◦
N and
44
◦
N, respectively) with a moderately warm climate. In our study, stream warming
downstream of BDAs was in safe range for westslope cutthroat and bull trout; no daily
temperatures within their lethal temperature range were observed. While stream warming
below natural beaver dams or BDAs occurring in moderate climates could exceed thermal
maxima for cold-water fish species, warming the thermal regime below BDAs in cool
climates of different hydrogeomorphic setting may bring streams closer to the thermal
optima of these fish species.
4.3. Implications of Warmed Waters for Fish
The unique BDA configurations used in this study mimicked the stream temperature
altering function of natural beaver dams. Overall, the BDAs we used increased the down-
stream temperatures, and warming increased with more BDAs in sequence. Noticeable is
that the overall stream temperature of the study reach in the cool climate of Rocky Moun-
tain was below 10
◦
C prior to BDA installations. Post-installation, the stream warmed
closer to the optimal thermal regime (13–15
◦
C) reported for local westslope cutthroat and
bull trout species. In comparison, beaver dams or BDAs installed in moderate climates
have been reported to warm downstream and/or exceed the thermal refugia even to a
lethal range of temperature. Therefore, in designing and installing BDAs, we need to
consider their overall ecological and hydrogeomorphic impacts and make sure decisions
on their installation balance both their positive and negative impacts. In terms of water
temperatures being affected by BDAs, they do something not particularly desirable—warm
the water. Furthermore, our results indicate that adding more BDAs in sequence warms
the water more. In the stream we studied, the warming was not so much that it became
too hot for the two threatened trout species. However, a lesson learned is that we need to
understand the suite of ecosystem changes that adding BDAs to a stream makes so that we
can take a holistic view of whether installing them will help meet overall restoration goal(s).
For example, in installing multiple BDAs in sequence, we need to balance the number
installed in sequence with their negative impact (warming) with the positive impacts on
streamflow moderation [Munir and Westbrook] [25].
Water 2021,13, 990 13 of 14
Author Contributions:
T.M.M.: Conceptualization, formal analysis, visualization, writing–original
draft preparation. C.J.W.: Conceptualization, methodology, supervision, funding acquisition, re-
sources, writing–review and editing. All authors have read and agreed to the published version of
the manuscript.
Funding:
Grants from the Natural Sciences and Engineering Research Council of Canada (NSERC)
Discovery (RGPIN-2017-05873) and CREATE (463960-2015) programs, the Global Water Futures
program, and Alberta Innovates Water Innovation Program (G2020000036) supported this research.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement:
Data that support the findings of this study are publicly archived at:
https://github.com/TariqMunir/Munir-Westbrook-Supplementary-Data_BDAs.git (accessed on
1 April 2021).
Acknowledgments:
We thank Greg Lewallen, Amanda Ronnquist, Uswah Aziz, Stephanie Streich
and Selena Schut for field assistance, and Greg Shyba and Reg Remple of the Ann and Sandy Cross
Conservation Area for logistical support. Field support was provided by the University of Calgary
Biogeosciences Institute.
Conflicts of Interest: The authors declare no conflict of interest.
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